The objective of the proposed project is the development of a cortical cooling probe and procedures by which the behavioral function of subdivisions of sensorimotor cortex in primates can be examined. More specifically, the tactile discrimination deficits associated with cryogenic depression of architectonic and physiologic subdivisions of sensorimotor cortex in the prosimian primate, Galago crassicaudatus, will be determined. In recent studies of galago, we defined the organization of cutaneous and joint related input from the hand to the cytoarchitectural fields of the sensorimotor region. By using cortical cooling to produce an acute reversible functional depression of separate subdivisions of sensorimotor cortex in galago during discrimination testing, we intend to determine the behavioral contribution of each division to tactile capacity. The effects of cooling on single neurons in sensorimotor cortex will be examined independently of the behavioral studies to measure the depression thresholds for both cutaneous and noncutaneous cells, and to measure the time course of depression and recovery following cortical cooling. In previous studies of the behavioral significance of subdivision of the primary somatic sensory area (SmI) in the simian species, Macaca mulatta, we found the surgical removal of cutaneous area associated with discrimination deficits on "texture" tasks and removal of noncutaneous area with deficits on "size" and "angle" tasks. The proposed study will examine this relationship between specific physiological input and specific discrimination capacity in galago by the selective cooling of sensorimotor divisions receiving predominantly one type input or the other, and by determining the depression thresholds for cutaneous and noncutaneous input in the SmI granular region. The development of an acute, reversible lesion technique has important potential for examination of behavioral function of subdivsions in sensorimotor cortex in other simian and porsimian species and in search for cortical areas contributing to recovery of tactile function in our studies of SmI-lesioned infant macaques.